#include <bits/stdc++.h>
using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");
int n;
int p;
int nr5;
int main()
{
    fin >> p;
    int j = 1;
    if (p == 0)
        fout << 1;
    else
    {
        while (nr5 < p)
        {
            n += 5;
            nr5++;
            if (j % 5 == 0)
            {
                int x = j;
                while (x % 5 == 0)
                {
                    x /= 5;
                    nr5++;
                }
            }
            j++;
        }
        fout << n;
    }
    fin.close();
    fout.close();
    return 0;
}